gRPC M0 R0.2: tag metadata over gRPC (GetTagInfosFromName, live-verified)

Routes HistorianClient.GetTagMetadataAsync over gRPC when Transport==RemoteGrpc,
via the new Grpc/HistorianGrpcTagClient calling RetrievalService.GetTagInfosFromName
(the plural string-handle metadata op).

- String handle = the Open2 storage-session GUID formatted uppercase (the format
  that resolves the native string-handle path); threaded out of the shared handshake
  via a new HistorianGrpcHandshake.Session { ClientHandle, StorageSessionId, StringHandle }.
- Request btTagNames = uint count + per-name(uint charCount + UTF-16LE) — golden-byte
  unit-tested (BuildTagNamesBuffer).
- Response btTagInfos = uint count + CTagMetadata records — decoded by the existing
  HistorianTagQueryProtocol.ParseGetTagInfoResponse; data type via the shared MapDataType.

The 2020 WCF string-handle wall does NOT apply on the gRPC front door, as the
string-handle-wall RE note predicted. LIVE-VERIFIED against a real 2023 R2 server:
GetTagMetadataAsync returns the requested tag with a valid decoded data type.

216 unit tests pass. Captured framing confirmed live then discarded; no tag names
or identities committed.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01B6mcaT2PjRFKcogzp9UkfC

tests/AVEVA.Historian.Client.Tests/HistorianGrpcIntegrationTests.cs

@@ -66,6 +66,26 @@ public sealed class HistorianGrpcIntegrationTests
         Assert.False(string.IsNullOrWhiteSpace(version));
     }
 
+    [Fact]
+    public async Task GetTagMetadataAsync_OverGrpc_ReturnsRequestedTag()
+    {
+        string? host = Environment.GetEnvironmentVariable("HISTORIAN_GRPC_HOST");
+        string? tag = Environment.GetEnvironmentVariable("HISTORIAN_TEST_TAG");
+        if (string.IsNullOrWhiteSpace(host) || string.IsNullOrWhiteSpace(tag)
+            || string.IsNullOrEmpty(Environment.GetEnvironmentVariable("HISTORIAN_USER")))
+        {
+            return;
+        }
+
+        HistorianClient client = new(BuildOptions(host));
+        HistorianTagMetadata? metadata = await client.GetTagMetadataAsync(tag, CancellationToken.None);
+
+        Assert.NotNull(metadata);
+        Assert.Equal(tag, metadata!.Name);
+        // A real metadata record decodes to a known data type (descriptor passed MapDataType).
+        Assert.True(Enum.IsDefined(metadata.DataType));
+    }
+
     private static HistorianClientOptions BuildOptions(string host)
     {
         string? user = Environment.GetEnvironmentVariable("HISTORIAN_USER");

tests/AVEVA.Historian.Client.Tests/HistorianGrpcTransportTests.cs

@@ -135,6 +135,23 @@ public sealed class HistorianGrpcTransportTests
         Assert.Equal("20.0.000", response.StrParameterValue);
     }
 
+    [Fact]
+    public void BuildTagNamesBuffer_EncodesCountThenLengthPrefixedUtf16Names()
+    {
+        // R0.2 request framing: uint count + per-name(uint charCount + UTF-16LE). Golden bytes.
+        byte[] buffer = AVEVA.Historian.Client.Grpc.HistorianGrpcTagClient.BuildTagNamesBuffer(["AB", "C"]);
+
+        byte[] expected =
+        [
+            0x02, 0x00, 0x00, 0x00,             // count = 2
+            0x02, 0x00, 0x00, 0x00,             // "AB" char count = 2
+            0x41, 0x00, 0x42, 0x00,             // 'A','B' UTF-16LE
+            0x01, 0x00, 0x00, 0x00,             // "C" char count = 1
+            0x43, 0x00                          // 'C' UTF-16LE
+        ];
+        Assert.Equal(expected, buffer);
+    }
+
     [Fact]
     public void OpenConnectionRequest_CarriesNativeOpen2BufferUnchanged()
     {